Peat Hydraulic Conductivity Research Articles

Water level variation at a beaver pond significantly impacts net CO2 uptake of a continental bog

Abstract. The carbon (C) dynamics of northern peatlands are sensitive to hydrological changes owing to ecohydrological feedbacks. We quantified and evaluated the impact of water level variations in a beaver pond (BP) on the CO2 flux dynamics of an adjacent, raised Sphagnum–shrub-dominated bog in southern Canada. We applied the CoupModel to the Mer Bleue bog, where the hydrological, energy and CO2 fluxes have been measured continuously for over 20 years. The lateral flow of water from the bog to the BP was estimated by the hydraulic gradient between the peatland and the BP's water level and the vertical profile of peat hydraulic conductivity. The model outputs were compared with the measured hydrological components, CO2 flux and energy flux data (1998–2019). CoupModel was able to reproduce the measured data well. The simulation shows that variation in the BP water level (naturally occurring or due to management) influenced the bog net ecosystem exchange (NEE) of CO2. Over 1998–2004, the BP water level was 0.75 to 1.0 m lower than during 2017–2019. Simulated net CO2 uptake was 55 gCm-2yr-1 lower during 1998–2004 compared to 2017–2019 when there was no BP disturbance, which was similar to the differences in measured NEE between those periods. Peatland annual NEE was well correlated with water table depth (WTD) within the bog, and NEE also shows a linear relation with the water level at the BP, with a slope of −120 gCO2-Cm-2yr-1m-1. The current modelling predicts that the bog may switch from CO2 sink to source when the BP water levels drop lower than ∼ 1.7 m below the peat surface at the eddy covariance (EC) tower, located on the bog surface 250 m from the BP. This study highlights the importance of natural and human disturbances to adjacent water bodies in regulating the net CO2 uptake function of northern peatlands.

Submarine Groundwater Discharge From Non-Tidal Coastal Peatlands Along the Baltic Sea

Submarine groundwater discharge (SGD) is an important pathway for water and materials within the land-ocean transition zone that can impact coastal environments and marine life. Although research from sandy shorelines has rapidly advanced in recent years, there is very little understanding of coastal areas characterized by a low hydraulic conductivity, such as carbon-rich coastal peatlands. The objective of this study was to determine the magnitude and location of terrestrial SGD to be expected from a non-tidal low-lying coastal peatland located along the Baltic Sea and to understand the controlling factors using numerical modeling. We employed the HYDRUS-2D modeling package to simulate water movement under steady-state conditions in a transect that extends from the dune dike-separated rewetted fen to the shallow sea. Soil physical properties, hydraulic gradients, geological stratifications, and topography were varied to depict the range of properties encountered in coastal peatlands. Our results show that terrestrial SGD occurs at the study site at a flux of 0.080 m2 d−1, with seepage rates of 1.05 cm d−1 (upper discharge region) and 0.16 cm d−1 (lower discharge region above submerged peat layer). These calculated seepage rates compare to observations from other wetland environments and SGD sites in the Baltic Sea. The groundwater originates mainly from the dune dike—recharged by precipitation and infiltration from ponded peatland surface water—and to a lesser extent from the sand aquifer. The scenario simulations yielded a range of potential SGD fluxes of 0.008–0.293 m2 d−1. They revealed that the location of terrestrial SGD is determined by the barrier function of the peat layer extending under the sea. However, it has little impact on volume flux as most SGD occurs near the shoreline. Magnitude of SGD is mainly driven by hydraulic gradient and the hydraulic conductivity of peat and beach/dune sands. Anisotropy in the horizontal direction, aquifer and peat thickness, and peatland elevation have little impacts on SGD. We conclude that SGD is most probable from coastal peatlands with high water levels, large Ks and/or a dune dike or belt, which could be an essential source for carbon and other materials via the SGD pathway.

The hydraulic conductivity of peat with respect to scaling, botanical composition, and greenhouse gas transport: Mini-aquifer tests from the Red Lake Peatland, Minnesota

Hydraulic conductivity (K) is a key but problematic parameter in groundwater models particularly those that simulate flow in weak, readily deformable media, such as peat deposits. As a result, K represents a critical source of error in models that couple hydrological processes with the carbon balance of peatlands, a globally important source for greenhouse gases. We therefore conducted mini-aquifer tests on two mesoscale bog landforms within the large 1300 km2 Red Lake Peatland of northern Minnesota. These tests offer the dual advantage of determining the fine-scale distribution of K within a large (>900 m3) model domain. In addition, the stress created by a 24 h pumping operation should be capable of mobilizing pools of biogenic gases thoughout a deep peat deposit. The pumping results were monitored by 24 to 38 wells in order to calibrate a 3D finite-volume groundwater model with the aid of PEST (Parameter Estimation Analysis). High K values were determined at a Bog Forest (10−5 to 10−6 m s−1) and Bog Lawn (10−3 to 10−4 m s−1) sites, throughout their deep (>4 m) peat profiles. These tests also detected vertically continuous zones of unexpectedly high or low K values in contrast to the horizontal bedding planes and increasing degree of decomposition with depth. The vertical K zones are suggestive of three different modes of bubble transport that either locally dilate or partially block the peat pores. In addition, the tests provided new insights on a conceptual model linking K to the development of all large (>20 km2) forested bog complexes in mid-continental boreal North America.

Measuring the Hydraulic Conductivity of Peats and Organic Clays with Various Characteristics

This paper discusses the hydraulic conductivity (k) of peat and organic clay as measured by laboratory and in-situ tests. The k of various peat soils and organic clay soils in Hokkaido, Japan, was investigated by the following tests: in-situ hydraulic conductivity test using a borehole, electric cone penetration test, oedometer test, and laboratory hydraulic conductivity test. The k of peat and organic clay dramatically decreases during consolidation. The index of change in k, which indicates consolidation-related changes in k, increases linearly with the increase in the in-situ void ratio and the ignition loss. The k of peat measured by oedometer test was found to range from approximately 1/20 to 1/180 of that measured by in-situ hydraulic conductivity test, which is considered to provide the macroscopic k of peat ground. Since large plant remnants must be removed for the oedometer testing of peat, the laboratory k obtained from this test underestimates the macroscopic k of the peat layer. The ratio of laboratory k to in-situ k can be simply expressed as a function of the ignition loss. Based on the results of a dissipation test of pore water pressure that used the electric cone penetration test, an equation for estimating the in-situ k of peat ground is presented. Using the above-mentioned experimental correlations, a suitable procedure for determining the permeability parameters of peat ground in practical applications is proposed.

Implications of Peat Soil Conceptualization for Groundwater Exfiltration in Numerical Modeling: A Study on a Hypothetical Peatland Hillslope

AbstractFully integrated physically based hydrological modeling is an essential method for increasing hydrological understanding of groundwater‐surface water (GW‐SW) interactions in peatlands and for predicting anthropogenic impacts on these unique ecosystems. Modeling studies represent peat soil in a simplistic manner, as a homogeneous layer of uniform thickness, but field measurements consistently show pronounced spatial variability in peatlands. This study evaluated uncertainty in groundwater levels and exfiltration fluxes associated with the simplified representation of the peat soil layer. For transferability of the results, impacts of selected topographical and hydrogeological conceptual models on GW‐SW exchange fluxes were simulated in a hypothetical hillslope representing a typical aquifer‐mire transect. The results showed that peat soil layer geometry defined the simulated spatial GW‐SW exchange patterns and groundwater flow paths, whereas total groundwater exfiltration flux to the hillslope and groundwater level in the peatland were only subtly altered by different conceptual peat soil geometry models. GW‐SW interactions were further explored using different scenarios and dimensionless parameters for peat hydraulic conductivity and hillslope‐peatland system slope. The results indicated that accurate representation of physical peat soil properties and landscape topography is important when the main objective is to model spatial GW‐SW exchange. Groundwater level in virtual peatland was not greatly affected by groundwater drawdown in an adjacent aquifer, but the magnitude and spatial distribution of GW‐SW interactions was significantly altered. This means that commonly used groundwater depth observations near peat‐mineral soil interfaces and within peatlands may not be a suitable indicator for monitoring the hydrological state of groundwater‐dependent peatland ecosystems.

Impacts of Groundwater Drainage on Peatland Subsidence and Its Ecological Implications on an Atlantic Raised Bog

AbstractField data of topography, water levels, and peat hydraulic conductivity collected over a 28‐year period have revealed the impacts of marginal drainage on uncut raised bog ecohydrology and its peat properties. Drainage of the regional groundwater body has induced changes in the hydraulic properties of deep peat, with peat compression decreasing hydraulic conductivity and storativity while simultaneously introducing localized secondary porosity and effective storage. Where peat has increased in hydraulic conductivity, there is a corresponding decline in vertical hydraulic gradients and significant localized increases in recharge to the underlying substrate. Repeated topographic surveys show intense localized areas of peat consolidation (>5%) where it is underlain by highly permeable (>10 m/day) glacial till deposits. More widely, continued subsidence (4–6 mm/year) of the bog surface has been measured over 900 m from the bog margin, resulting in the progressive loss of approximately 40% of actively growing raised bog since 1991. This loss has thus been shown to be attributable to changes in the underlying groundwater head due to deep‐cut drainage, rather than near‐surface peatland drainage. However, although reinstating regional hydrostatic pressures in order to restore this ombrotrophic peatland may control the rapid drainage through preferential flow pathways, this may not eliminate the ecological impacts resulting from changed surface morphology arising from subsidence. Hence, this longitudinal study provides new insights into the role that aquifer systems and groundwater bodies play in maintaining hydrogeological processes in ombrotrophic peatland systems, while highlighting the difficulty in ecological restoration where regional groundwater dependencies are significant.

Assessing rainfall pattern, groundwater level, and peat hydraulic conductivity for effective peat prevention measure

Severe drought and less precipitation during a prolonged dry season and El-Nino events has been observed as a main trigger of the decrease of groundwater level leads to the dryness of the degraded peat and exacerbates burning conditions. To get a better understanding of this issue, we studied fire conditions in a portion of the ex-Mega Rice Project (MRP) area, Central Kalimantan. Here, we examine fire season and hydrology factors affecting peat fires by using Terra/Aqua MODIS hotspots dataset and groundwater level data from 300 dipwells and 15 staff gauges established in the MRP area. We use the Interpolation Data Weighting (IDW) to explain the fire risk in the area based on its hydraulic conductivity. Our results clearly show that even the moderate to high rainfall intensity is not enough to rewet the dry-degraded peat and thus to leave them in dry condition. Here, we highlight the importance of considering the rainfall pattern of previous successive dry and rainy season for fire risk assessment. Most of the fires occurred in the area between 1.1×10−6 and 2.1×10−6 cm/s hydraulic conductivity and below -10 cm groundwater level, sharply pointing out the importance to keep degraded peat in wet condition for fire prevention.

Hydraulic conductivity of peat in Western Siberia

The paper aims at estimating hydraulic conductivity of peat. It is a complicated process since peat has some unique properties that are not typical for mineral soils. Other difficulties involve the lack of elaborated procedure for laboratory testing and data processing, high sensitivity of peat soils to external and internal factors; which leads to considerable fluctuation in peat hydraulic conductivity values. The specific properties of hydraulic conductivity in peat soils are proved by numerous experimental data. The article also provides the permeability values for the most typical peat species in Western Siberia. The obtained data allow forecasting peat soil response to the development of peatlands.

Exploring pathways to late Holocene increased surface wetness in subarctic peatlands of eastern Canada

AbstractThe poor fens of the Laforge region, northeastern Canada, have developed under subarctic conditions. They are characterized by a microtopography of large pools and low, narrow strings. Paleorecords suggest some of these systems were once ombrotrophic and relatively dry. Taking account of their current bioclimatic position, we aimed to explore the possible pathways towards the current wet state, a process referred to as “aqualysis”. We combined paleoecological methods applied to a peat core with conceptual modelling to identify factors that might plausibly explain aqualysis. Reconstructions showed the Abeille peatland became minerotrophic with high water tables between 2400 and 2100 cal yr BP. Conceptual modelling, supported by simulations using the numerical DigiBog model, allowed us to identify the effects of cooling and increased precipitation on productivity, decay, peat hydraulic conductivity and vertical peat accumulation. Both cooling and increased precipitation were required for aqualysis to occur and for wet surface conditions to persist to the present day. Increased recharge from the catchment, which also restricted drainage from the peatland center laterally, was likely critical for the development of minerotrophic conditions. The scenario of cooling and wetting in these peatlands is supported by available paleoclimate records for eastern Canada.

Evaluating the hydraulic and transport properties of peat soil using pore network modeling and X-ray micro computed tomography

Micro-scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far. Characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands. As opposed to the common macro-scale (or bulk) representation of groundwater flow and transport processes, a pore network model (PNM) simulates flow and transport processes within individual pores. Here, a pore network modeling code capable of simulating advective and diffusive transport processes through a 3D unstructured pore network was developed; its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics (CFD) simulations. This is the first time that peat pore networks have been extracted from X-ray micro-computed tomography (µCT) images of peat deposits and peat pore characteristics evaluated in a 3D approach. Water flow and solute transport were modeled in the unstructured pore networks mapped directly from µCT images. The modeling results were processed to determine the bulk properties of peat deposits. Results portray the commonly observed decrease in hydraulic conductivity with depth, which was attributed to the reduction of pore radius and increase in pore tortuosity. The increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth, which extended the flow path of fluid particles. Results also revealed that hydraulic conductivity is isotropic locally, but becomes anisotropic after upscaling to core-scale; this suggests the anisotropy of peat hydraulic conductivity observed in core-scale and field-scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils. Transport simulations revealed that for a given solute, the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity. Longitudinal dispersivity of peat also was computed by analyzing advective-dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil; it is not sensitive to soil depth and does not vary much along the soil profile.

Water‐level dynamics in natural and artificial pools in blanket peatlands

AbstractPerennial pools are common natural features of peatlands, and their hydrological functioning and turnover may be important for carbon fluxes, aquatic ecology, and downstream water quality. Peatland restoration methods such as ditch blocking result in many new pools. However, little is known about the hydrological function of either pool type. We monitored six natural and six artificial pools on a Scottish blanket peatland. Pool water levels were more variable in all seasons in artificial pools having greater water level increases and faster recession responses to storms than natural pools. Pools overflowed by a median of 9 and 54 times pool volume per year for natural and artificial pools, respectively, but this varied widely because some large pools had small upslope catchments and vice versa. Mean peat water‐table depths were similar between natural and artificial pool sites but much more variable over time at the artificial pool site, possibly due to a lower bulk specific yield across this site. Pool levels and pool‐level fluctuations were not the same as those of local water tables in the adjacent peat. Pool‐level time series were much smoother, with more damped rainfall or recession responses than those for peat water tables. There were strong hydraulic gradients between the peat and pools, with absolute water tables often being 20–30 cm higher or lower than water levels in pools only 1–4 m away. However, as peat hydraulic conductivity was very low (median of 1.5 × 10−5 and 1.4 × 10−6 cm s−1 at 30 and 50 cm depths at the natural pool site), there was little deep subsurface flow interaction. We conclude that (a) for peat restoration projects, a larger total pool surface area is likely to result in smaller flood peaks downstream, at least during summer months, because peatland bulk specific yield will be greater; and (b) surface and near‐surface connectivity during storm events and topographic context, rather than pool size alone, must be taken into account in future peatland pool and stream chemistry studies.

FIELD HYDRAULIC CONDUCTIVITY OF SOME MALAYSIAN PEAT

Field measurements on the hydraulic conductivity (K) of several developed and undeveloped peat soils using auger hole method were conducted. Developed deep peat has hydraulic conductivity values in the range of 6.32x 10-4 to 4.44 X 10-3 (0.55 to 3.84 mid). The studies also indicated that developed shallow peat has a conductivity value of 5.55xlO-4 to 5.67xI0-3 cm/s (0,48 to 4.90 mid), while shallow undeveloped peat K value was in the range of 9.24xlO-4 to 1.92x10-3 cmls (0.80 to 1.66 mid). The values of peat hydraulic conductivity's were found to be difficult to relate with their depth and development stages . This is because a number of uncertain variables such as the capillary potential, the existence of macro and micro-pores and their tortuosity are difficult to measure. These variables can definitely contribute to the K value of peat.

Relationships between vegetation type, peat hydraulic conductivity, and water table dynamics in mountain fens

AbstractThe ecohydrologic function of fens is characterized by feedbacks between biological and hydrologic processes. Vegetation composition is one important factor that is both responsive to the site hydrologic regime and, by providing the organic material that determines peat hydrophysical properties, influences hydrologic conditions. In this study, we investigated the relationship between vegetation type and peat soil hydraulic conductivity in fen wetlands within the Rocky Mountain National Park, Colorado. We used ponded infiltration tests to estimate the saturated hydraulic conductivity of near‐surface peat in mountain fens with differing vegetation, including large‐sedge fens dominated by Carex aquatilis and Carex utriculata, small‐sedge fens dominated by Eleocharis quinqueflora, and fens with an abundance of woody plants and mosses. Estimated hydraulic conductivities were lowest at the fens dominated by E. quinqueflora, with a median value of 1·3 × 10−3 cm s−1 compared with 1·3 × 10−2 and 9·6 × 10−3 cm s−1, respectively, at the large‐sedge and woody fens. These data help explain historical water table observations at each fen. The E. quinqueflora‐dominated fens in our study area maintain a high water table with saturated conditions throughout the summer growing season. Other fens with higher‐conductivity peat show a more dynamic water table that is below ground surface by late summer. Copyright © 2015 John Wiley & Sons, Ltd.

Bridging the gap between models and measurements of peat hydraulic conductivity

AbstractPeat saturated hydraulic conductivity, Ksat, declines strongly with increasing degree of decomposition, providing a potentially important negative ecohydrological feedback that may buffer peatlands from climate‐induced drying. However, the quantitative nature of this relationship is poorly understood. We measured downcore changes in Ksat and carbon‐to‐nitrogen concentration quotients (C/N) in 14 shallow (∼0.5 m deep, 0.1 m diameter) peat cores from a Swedish raised bog. We used the C/N measurements to approximate the fraction of original peat mass remaining. A linear mixed effects (LME) model predicts log10(Ksat) from (i) our C/N‐derived estimate of fractional remaining mass; (ii) depth; (iii) microhabitat (hummock, hollow); and (iv) location (treeless bog center, treed bog margin). The LME model indicated no significant random effects or interactions between predictors, so we derived a nonlinear multiple regression (NLMR) model to predict Ksat on its original scale. Both LME and NLMR models predict that Ksat decreases exponentially with depth and that Ksat is lower beneath hollows than beneath hummocks for equivalent depths below the surface. Fractional remaining mass was an important predictor in the LME model, but not in the NLMR model. The distinction between central and marginal areas of the bog was not an important predictor. We demonstrate for the first time that the relationship between fractional remaining mass and Ksat is log‐linear, and suggest revisions that should be made to peatland development models. In particular, depth—usually ignored in modeling studies—exerted a strong control over Ksat independently of decomposition and should be included explicitly in model algorithms.

Hydrology and hydraulics of treatment wetlands constructed on drained peatlands

Treatment wetlands are considered best management practice as they can remove nitrogen, phosphorus and suspended solids from peat extraction or forestry runoff. Treatment wetlands are established on intact or formerly drained peatlands after restoration of the site hydrology by ditch blocking or other methods. However, drainage changes the physical properties of peat, so the hydraulic and hydrological conditions in peatlands may change. Consequently, treatment wetlands constructed on drained areas may have short residence times, resulting in poor purification results. This study determined the hydrological and hydraulic characteristics of treatment wetlands constructed on drained peatlands by studying peat hydraulic conductivity and water distribution in 20 different wetlands in Finland. Four wetlands were studied in more detail using tracer tests, water balance and continuous groundwater measurements. More than 50% of the drained treatment wetlands studied had a lower active flow depth layer (only 10 or 20cm) with higher hydraulic conductivity (K) than normally found in pristine peatlands. At 25% of the sites, K was high at all depths investigated (down to 60–70cm). At several sites, the water was unequally distributed across the wetland surface, indicating that only part of the wetland was being used for purification. The residence time, as determined by tracer tests, varied significantly between sites. These results indicate that past drainage still influences the hydraulics of treatment wetlands.

Peat deformation and biogenic gas bubbles control seasonal variations in peat hydraulic conductivity

AbstractThe hydraulic conductivity (K) of peat beneath the water table varies over short (annual) periods. Biogenic gas bubbles block pores and reduce K, and seasonal changes in the water table position cause peat deformation, altering peat pore size distribution. Although it has been hypothesized that both processes reduce K during warm dry summer conditions, temporal variations in K under field conditions have been explained previously by peat volume changes (strain) alone. We determine the effect of both controls on K by monitoring changes in gas content (Δγ), strain and K within a poor fen. Over the growing season, K decreased by an order of magnitude. In the near‐surface peat (0.3–0.7 m), this reduction is more strongly correlated with Δγ, providing the first field‐based evidence that biogenic gas bubbles reduce K. In the deeper peat (0.7–1.3 m), K is correlated principally with strain. However, causality is uncertain because of multicollinearity between strain and Δγ. To mitigate for multicollinearity, we took advantage of a peatland drainage experiment where the water table was artificially dropped at the beginning of the growing season, reducing correlations between strain and Δγ. Δγ remained the primary cause of K variations just beneath the water table at a depth of 0.5–0.7 m, although further down through the peat profile (0.7–1.2 m) changes in K were controlled by strain. We suggest that the larger pore structure of the poorly decomposed peat just below the water table is impacted less by volume changes than that of the more decomposed peat at depth. However, within this poorly decomposed peat, K is reduced by the high gas contents that result from higher rates of methane production. Copyright © 2012 John Wiley & Sons, Ltd.

Groundwater–surface water interaction between an esker aquifer and a drained fen

Summary Groundwater discharge from an esker aquifer to a fen was studied to understand relevant hydrological processes for groundwater-surface water interaction in an esker–peatland hillslope. Piezometric levels of the peat layer and esker sand layer were continuously monitored and compared to climate data. Groundwater exfiltration points were spatially mapped and related to peat depth. The study showed a clear interaction between fen surface water and sand esker groundwater although the hydraulic conductivity of peat was low and the peat depth thick. In the artesian aquifer beneath the fen, the piezometric head showed a clear response to precipitation and evapotranspiration. Wetting of the peat is rapidly seen as pressure increase in the confined aquifer. This provides new information on hydraulics of wetlands found in aquifer discharge areas. Groundwater exfiltrated through thick peat layers in vertical preferential point discharges demonstrating how double porosity provides flow through the peat layer with low hydraulic conductivity in the peat matrix. The “pipe flow” channels were found in the deep peat area in the transition zones from deep peat to shallow peat. Diffuse seepage through the ditch bottom was found where ditches cut into the sand layer. Increased discharge through the ditch bed reduced the flow resistance at the aquifer boundary which can lower the groundwater level in the esker. The results show new processes in the groundwater discharge zone that are useful for groundwater modelling and policy development for future groundwater protection.

The DigiBog peatland development model 2: ecohydrological simulations in 2D

ABSTRACTIn the first of this pair of papers we introduced the conceptual and hydrological basis of the peatland development model—DigiBog. Here we describe the submodels which simulate (i) the production of plant litter, (ii) peat decomposition, and (iii) changes in peat hydraulic conductivity due to decomposition. To illustrate how the model works, DigiBog was applied to three example situations: Bogs 1, 2, and 3. For each, the net rainfall was held constant at 30 cm year−1 and the oxic decomposition parameter kept at 0·015 year−1. The anoxic decomposition parameter varied from 5 × 10−6 (Bog 1) to 5 × 10−4 year−1 (Bog 3). Peatland development was simulated for 5000 years. For Bogs 1 and 2, plausible large peatland domes develop. Despite having a higher anoxic decomposition rate, Bog 2 grew thicker than Bog 1. This apparently counter‐intuitive result is caused by the feedback between hydraulic conductivity and degree of peat decomposition. For both Bogs 1 and 2, DigiBog also simulates transitions from wet to dry states, demarked by sudden switches from poorly decomposed to well‐decomposed peat moving upwards in the peat profile. These regime shifts result from internal peatland dynamics and not from allogenic influences, and challenge the view that peat properties are always a reflection of climate. In Bog 3, a ‘mini‐bog’ developed and persisted near the margin of the peatland; this bog can also be explained in terms of the internal feedbacks within the model. Copyright © 2011 John Wiley & Sons, Ltd.

A new model of Holocene peatland net primary production, decomposition, water balance, and peat accumulation

Abstract. Peatland carbon and water cycling are tightly coupled, so dynamic modeling of peat accumulation over decades to millennia should account for carbon-water feedbacks. We present initial results from a new simulation model of long-term peat accumulation, evaluated at a well-studied temperate bog in Ontario, Canada. The Holocene Peat Model (HPM) determines vegetation community composition dynamics and annual net primary productivity based on peat depth (as a proxy for nutrients and acidity) and water table depth. Annual peat (carbon) accumulation is the net balance above- and below-ground productivity and litter/peat decomposition – a function of peat hydrology (controlling depth to and degree of anoxia). Peat bulk density is simulated as a function of degree of humification, and affects the water balance through its influence on both the growth rate of the peat column and on peat hydraulic conductivity and the capacity to shed water. HPM output includes both time series of annual carbon and water fluxes, peat height, and water table depth, as well as a final peat profile that can be "cored" and compared to field observations of peat age and macrofossil composition. A stochastic 8500-yr, annual precipitation time series was constrained by a published Holocene climate reconstruction for southern Québec. HPM simulated 5.4 m of peat accumulation (310 kg C m-2) over 8500 years, 6.5% of total NPP over the period. Vascular plant functional types accounted for 65% of total NPP over 8500 years but only 35% of the final (contemporary) peat mass. Simulated age-depth and carbon accumulation profiles were compared to a radiocarbon dated 5.8 m, c.9000-yr core. The simulated core was younger than observations at most depths, but had a similar overall trajectory; carbon accumulation rates were generally higher in the simulation and were somewhat more variable than observations. HPM results were sensitive to century-scale anomalies in precipitation, with extended drier periods (precipitation reduced ∼10%) causing the peat profile to lose carbon (and height), despite relatively small changes in NPP.

A Review on Hydraulic Conductivity and Compressibility of Peat

This study reviews the results of several experimental and field investigations on the behavior of peat in hydraulic conductivity and compressibility. A study on the mechanical properties of peat is important in order to gather sufficient information on the response of the soil to preloading in terms of the soil permeability and deformation. Preloading technique is normally employed as a method to improve peat ground so that the improved ground can be used as a soil foundation to support road embankment. Findings on the initial hydraulic conductivity of peat revealed that the initial coefficient of vertical permeability (kv0) of the soil ranged from 10-5 to 10-8 m sec-1 with the value was found to be lower in amorphous peat as compared to that of fibrous peat. Such findings indicated that the initial hydraulic conductivity of peat is influenced by the soil degree of decomposition. The higher is the soil degree of decomposition, the lower is its initial rate of hydraulic conductivity. Results from oedometer tests on Portage peat showed that while the soil coefficient of secondary compression (cI±1) ranged from 0.17 to 0.18, its coefficient of tertiary compression (cI±2) varied from 0.6 to 0.18. At high consolidation pressure, the soil cI±1 approached its cI±2 indicating the merging of secondary and tertiary compression components. It can be concluded that the behavior of peat is different from that of inorganic soil in that it exhibited high to moderate initial hydraulic conductivity, rapid primary consolidation and large secondary compression.